In a device manufacturing process using a semiconductor wafer, various kinds of processing, e.g., polishing, film production, etching, ion implantation, cleaning, a heat treatment, exposure, coating, and bonding are performed to a silicon wafer which is a material. A defect is produced during a plurality of such processes in some situation, and it degrades quality of a final product but also adversely affects subsequent processes in some cases. The defect which affects the quality or the processes is called a killer defect, and a wafer in which even one killer defect is produced may be determined to be a defective product as a whole. In a case where the wafer becomes a defective product after subsequent processes due to a killer defect produced in an initial process in particular, costs concerning the subsequent processes are all lost.
To avoid such a situation, a wafer containing a killer defect is sorted out at a halfway stage. In general, a sorting method using a laser surface inspection apparatus is adopted, and there are, e.g., SP1, SP2, and SP3 manufactured by KLA-Tencor Corporation as the apparatus. These apparatuses detect scattering light from a defect, can perform high-speed processing, and have characteristics of high sensitivity.
On the other hand, on a wafer surface, there are killer defects as well as foreign matters adhering to the surface. Since they can be easily removed by subsequent cleaning, their influence on final quality of the wafer is slight, but discrimination from the killer defects cannot be effected in a halfway inspection using the laser surface inspection apparatus, which may lead to false recognition as defects. This case corresponds to overkill, and a loss as a material is produced. Thus, in the inspection conducted during a halfway process, highly accurately discriminating between the killer defects and the foreign matters is important. Although there is an inspection method for performing highly accurate discrimination by direct observation of high magnification, there is generally a limit in processing speed, and an inspection frequency is restricted.
Thus, as a method for improving a classification accuracy of an LPD (Light Point Defect) which is detected by the laser surface inspection apparatus, a distribution method using a plurality of pieces of detection angle information has been suggested. A surface is irradiated with a laser beam from an obliquely upper direction while scanning a wafer, detection of a signal of light which scatters in a high-angle direction is determined as DNO (low-angle incidence/high-angle detection), detection of a signal of light which scatters in a low-angle direction is determined as DWO (low-angle incidence, low-angle detection), and respective calculated LPD sizes are compared with each other, thereby performing classification. It is to be noted that D is an initial of Darkfield, and it means dark field inspection.
For example, Patent Document 1 discloses a method for classifying a particle and a microscratch by using an LPD size ratio of DWO and DNO. Patent Document 2 discloses that a crystal defect and a foreign matter are classified by using an LPD size ratio of DWO and DNO. Patent Document 3 discloses that a pit and a protrusion are classified by using an LPD size ratio of DWO and DNO. Patent Document 4 discloses that a defect and a foreign matter are classified by using an LPD size ratio of DWO and DNO.